Electrical circuits that are fabricated on semiconductor wafers can include a plurality of voltage domains. A voltage domain is an electrical circuit or circuit block that operates at a specific supply voltage value. The supply voltages for circuits that are used in mobile terminal devices are typically derived from a battery voltage. The supply voltage for a voltage domain is usually connected by means of a switching unit that is arranged outside of a semiconductor device. For this purpose, a voltage source such as a battery that provides the supply voltage is coupled to a supply connection or a supply pin of the semiconductor device via the switching unit. The supply connection is connected to a voltage network within the semiconductor device and forms a voltage domain. The supply connection is connected to or isolated from the voltage source in accordance with a switching state that is selected for the switching unit. If the supply connection is connected to the voltage source, the supply voltage is present at the voltage domain.
In typical systems, a control signal for connecting or disconnecting the supply voltage from a voltage domain is generated within the semiconductor device. In order to control the switching unit by means of the control signal, a control connection or control pin to pass the control signal to the switching unit is provided at the semiconductor device. As a result, at least two connections are needed at the semiconductor device for each voltage domain. The number of connections or pins available for a semiconductor device can be limited as typically many connections are required for other functions. As a result, a disadvantage of this approach is that only a limited number of voltage domains may be able to be provided within the semiconductor device.
It is known to provide a switching unit with respect to each voltage domain within the semiconductor device. The respective switching unit enables the supply voltage to be disconnected from or connected to the voltage domain. The switching unit is typically implemented as a switching element that is large in relation to other circuits that are used in the semiconductor device in order to drive large currents without significant voltage drops at the voltage domains. Furthermore, the switching element is typically located within regions of the semiconductor device or circuit that are not fabricated by means of standard cells. As a result, the length of a supply line between a switching element and a voltage domain may result in a significant voltage drop across the supply line.
In order to avoid the voltage drops, the large switching element is often implemented with multiple switching elements that are relatively smaller in size. The smaller switching elements can be designed and implemented as standard cells. A number of switching elements can be connected in parallel in order to meet the current demands of a voltage domain.
A plurality of voltage domains are usually coupled to voltage supply. When a connection is first made to a first voltage domain, current flows that initially charges the gates and/or other capacitances of circuits within the first voltage domain. This connection operation can initially give rise to a relatively large change in a current ISUP supplied by the voltage supply. The supply lines arranged between the voltage supply and the voltage domain typically have an inductance L. As a result of this inductance, a change in the current ISUP causes a voltage drop ΔUSUP that occurs along the supply lines in accordance with Equation (1).
                              Δ          ⁢                                          ⁢                      U            SUP                          =                              L            ⁢                                          ⅆ                                  I                  SUP                                                            ⅆ                t                                              +                                    RI              SUP                        .                                              (        1        )            
A non-reactive resistance R that is present in the supply lines is also taken into account by Equation (1).
In most cases, at least one second voltage domain is connected to a supply line and a same supply voltage is provided to the first and second voltage domains. If the second voltage domain is already in an operating state when the first voltage domain is switched on, the voltage drop ΔUSUP may be large enough to result in a local malfunction within the second voltage domain. The local malfunction can lead to a global malfunction of the entire semiconductor device. The occurrence of a global malfunction is often times not immediately evident to a user of the semiconductor device.
For these and other reasons, there is a need for the present invention.